Articles known as pneumatic or gas springs, which for convenience can be referred to as counterbalance links are becoming more and more common in commercial articles, particularly in the automotive industry, but they are being used in many other fields wherever the need is present to provide a counterbalance force for closure units, such as lids, doors and cabinet fronts, and gas spring replacement for mechanical spring fittings is becoming prevalent. In some fields of use, such as automotive, the range of change of the surrounding temperature can be substantial. When the temperature drops, the pressure of the gas within the spring unit drops and concurrently therewith the force holding the piston rod extended or in the hold-open position must drop, and often drops below that required to hold the closure member (hatchback) in an open position. Conversely, at higher temperatures the force is often too high. To counter these disadvantages, the industry has evidenced a desire to have pneumatic springs which in some manner will have their output force compensated for temperature changes.
Insofar as applicants are aware, there has been no previously known structure pertaining to the present pneumatic spring invention with its temperature compensation features. These are prior art shock absorbers using liquid which have temperature compensating aspects but most function on pressure changes due to viscosity changes of the liquid under various temperature conditions, and examples are seen in the following U.S. Patents: Pat. No. 1,797,799 to L. W. Shutts for Shock Absorber; Pat. No. 2,301,318 to R. F. Peo for Thermostatic Bypass Valve; Pat. No. 3,674,120 to R. S. Johnson for Auxiliary Shock Absorber Damping Valves; and a German Published Application No. 2,051,858, dated May 25, 1972 to R. Gabler for Hydraulic Telescopic Damper. U.S. Pat. No. 3,147,967 to A. Bougeard for Pneumatic Shock Absorber and U.S. Pat. No. 3,444,830 to H. P. Doetsch for an Adjustable Gas Spring Supported Drawing Table show compensation between two chambers but neither of these patents teach temperature compensation in the pneumatic devices.